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Chapter 2 – Planet Earth
Section Notes
Video
Earth and the Sun’s Energy
Water on Earth
The Land
Impact of Water on Earth
Close-up
The Water Cycle
Ring of Fire
Earth’s Plates
India: Physical
Physical Map
World Almanac
Images
Major Eruptions in the Ring of
Fire
Quick Facts
Chapter 2 Visual Summary
Maps
Solar Energy
The Seasons: Northern
Hemisphere
Plate Separation
Plate Collision
Mount Saint Helens Eruption
Earth and the Sun’s Energy
The Big Idea
Earth’s movement and the sun’s energy interact to create
day and night, temperature changes, and the seasons.
Main Ideas
• Earth’s movement affects the amount of energy we
receive from the sun.
• Earth’s seasons are caused by the planet’s tilt.
Main Idea 1:
Earth’s movement affects the amount of
energy we receive from the sun.
• All life on Earth requires solar energy, or
energy from the sun, to survive.
– Amount of solar energy received changes
constantly
– Earth’s rotation, revolution, tilt, and latitude all
affect the amount of solar energy Earth receives.
Rotation and Revolution
Rotation
Revolution
• Earth spins on its axis—
an imaginary line that
runs through the center
of the planet around
which it turns.
• Earth follows an orbit, or
path, around the sun.
• It takes Earth 24 hours
to make one rotation,
or complete spin on its
axis.
• As Earth spins, different
parts of the planet face
the sun, thus causing
the changes from day to
night.
• Orbit is not a perfect
circle.
• It takes Earth 365¼
days to complete one
revolution, or trip
around the sun.
• Our calendar year is
based on the time it
takes Earth to complete
its orbit.
Tilt and Latitude
Tilt
Latitude
• Earth’s axis is tilted at
an angle of 23½
degrees from vertical.
• Latitude is the distance
north or south of Earth’s
equator.
• At any give time of
year, some places on
Earth tilt toward the
sun, and others tilt
away.
• Low-latitude areas,
those nearest the
equator, receive direct
rays from the sun all
year.
• Places tilting toward the
sun receive more solar
energy and have
warmer temperatures
than those that tilt
away.
• High-latitude areas,
those farther from the
equator, receive indirect
rays from the sun and
have colder
temperatures.
Main Idea 2:
Earth’s seasons are caused by the
planet’s tilt.
• Seasons are periods during the year that are
known for a particular type of weather.
– Many places experience four seasons—winter,
spring, summer, and fall.
– In some parts of the world, seasons are based on
the amount of rainfall
The Seasons
Winter and
Summer
Spring and Fall
Rainfall and
Seasons
• Earth tilts away
from sun in
winter and
towards the sun
in summer.
• In spring, Earth
begins to tilt
toward sun,
solar energy
increases,
temperatures
rise, and days
grow longer.
• In the tropics,
regions close to
the equator,
seasons are
marked by
rainfall rather
than
temperature.
• In fall, the
opposite occurs.
• At certain times
of year, winds
bring either dry
or moist air to
the tropics,
creating wet
and dry
seasons.
• Because of the
Earth’s tilt, the
Northern and
Southern
hemispheres
experience
opposite
seasons.
Water on Earth
The Big Idea
Water is a dominant feature on Earth’s surface and is
essential for life.
Main Ideas
• Salt water and freshwater make up Earth’s water supply.
• In the water cycle, water circulates from Earth’s surface to
the atmosphere and back again.
• Water plays an important role in people’s lives.
Main Idea 1:
Salt water and freshwater make up Earth’s
water supply.
Earth’s Water • Water covers some two-thirds of the planet.
• About 97 percent of the Earth’s water
• Unsafe to drink because of high levels of salt
Salt Water • In general, found in Earth’s oceans, which
cover some 71 percent of the planet’s surface
• Also found in some of Earth’s lakes
Freshwater
• Water without salt
• Makes up only 3 percent of our water supply
Freshwater
• Much of Earth’s freshwater is locked in glaciers, large areas of
slow moving ice, and in the ice of the Arctic and Antarctic
regions.
• Surface water is water that is found in Earth’s streams, rivers,
and lakes.
– Less than one percent of Earth’s water supply
– Streams, rivers, and lakes are common sources.
• Precipitation is water that falls to Earth’s surface as rain, snow,
sleet, or hail.
– Streams form when precipitation collects in a narrow channel and
flows toward the ocean.
• Most available freshwater is groundwater, water found below
Earth’s surface.
– Some naturally bubbles from the ground to the surface as a spring.
– Most obtained by digging wells
Main Idea 2:
In the water cycle, water circulates from
Earth’s surface to the atmosphere
and back again.
•
Water is the only substance on Earth that occurs naturally as a
solid, a liquid, and a gas, or water vapor.
•
The water cycle is the movement of water from Earth’s
surface to the atmosphere and back ; it is driven by the sun’s
energy.
–
Evaporation—water turns from liquid to gas.
–
Condensation—the rising gas cools and condenses, or changes from
a vapor into tiny liquid droplets, to form clouds.
–
Precipitation—if the droplets in clouds become heavy enough, they
fall back to Earth as rain, snow, sleet, or hail.
–
Runoff—excess water that isn’t absorbed as groundwater flows over
land and collects in streams, rivers, and oceans.
Main Idea 3:
Water plays an important role in
people’s lives.
Water Problems
Water Benefits
• Lack of available
freshwater, which
can be caused by
droughts or overuse
• Provides us with food to
eat
• Contaminated, or
polluted, water can
harm humans,
plants, and animals.
• Provides us with
recreation, including
swimming, fishing,
surfing, and sailing
• Flooding can
damage property
and threaten lives.
• Important source of
energy
The Land
The Big Idea
Processes below and on Earth’s surface shape the planet’s
physical features.
Main Ideas
• Earth’s surface is covered by many different landforms.
• Forces below Earth’s surface build up our landforms.
• Forces on the planet’s surface shape Earth’s landforms.
• Landforms influence people’s lives and culture.
Main Idea 1:
Earth’s surface is covered by many different
landforms.
• Landforms, or shapes on the planet’s surface, make up
the landscapes that surround us.
• Earth’s surface is covered with landforms of many
different shapes and sizes.
– Mountains, land that rises higher than 2,000 feet
– Valleys, areas of low land located between mountains or hills
– Plains, stretches of mostly flat land
– Islands, areas of land completely surrounded by water
– Peninsulas, land surrounded by water on three sides
Main Idea 2:
Forces below Earth’s surface build up our
landforms.
Earth’s Plates
• The planet’s continents, or large landmasses, are part of Earth’s
crust—the solid outer layer of the planet.
• Theory of plate tectonics suggests that Earth’s surface is divided
into a dozen or so slow-moving plates, or pieces of Earth’s crust.
Movement of Continents
• The idea that continents have traveled great distances over millions
of years is known as continental drift.
• Theory, developed by Alfred Wegener, states that the continents were
once united in a single supercontinent and over time, slowly
separated and moved to their present positions.
• As plates collide, separate, and slide, they shape Earth’s landforms
Pangea
Plates Collide, Separate, and Slide
Plates Collide
• Two ocean plates:
one pushes under
the other, creating
ocean trenches, or
deep valleys in
ocean floor
• Ocean and
continental plate:
ocean plate drops
beneath continental
plate, forcing land
above to crumple
and form mountain
range
• Two continental
plates:
land pushes up to
form mountains
Plates Separate
Plates Slide
• As plates move
apart, gaps between
plates allow magma
to rise to Earth’s
crust.
• As plates pass by
each other, they
sometimes grind
together, producing
earthquakes,
sudden, violent
movements of
Earth’s crust.
• Lava, magma that
reaches the Earth’s
surface, emerges
from the gap.
• As lava cools, it
builds a mid-ocean
range, or
underwater
mountain, that can
rise above the
surface of the ocean
to form islands.
• Earthquakes often
take place along
faults, or breaks in
Earth’s crust where
movement occurs.
• The region around
the Pacific plate,
called the Ring of
Fire, is home to
most of the world’s
earthquakes and
volcanoes.
Main Idea 3:
Forces on the planet’s surface shape
Earth’s landforms.
• Weather, water, and other forces change Earth’s
landforms by wearing them away or reshaping them.
• Weathering is the process by which rock is broken down
into smaller pieces called sediment.
– Heating and cooling can cause rocks to crack.
– Expansion of water as it freezes can cause cracks to expand.
– Roots of trees can pry rocks apart.
• Erosion is the movement of sediment from one location
to another.
– Can wear away or build up landforms
Types of Erosion
Wind Erosion
• Winds lift sediment
into air and carry it
across great
distances .
• On beaches and in
deserts, deposits
can form dunes.
• Blowing sand can
wear down rock.
Glacial Erosion
Water Erosion
• Glaciers, or large,
slow-moving sheets
of ice, erode the
land by carving
valleys and
mountain peaks.
• Waves and flowing
water can cut
through rock, carry
sediment, and
deposit sediment in
new locations.
• Crush rock into
sediment and move
it great distances
• Floodplains are
created when rivers
flood their banks
and deposit
sediment.
• Sediment carried by
a river all the way
to the sea creates a
delta.
Main Idea 4:
Landforms influence people’s lives and
culture.
Landforms can influence where people settle.
Landforms often influence what jobs are available in a region.
Landforms can affect language.
People sometimes change landforms to suit their needs.
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